1. Field of the Invention
This invention relates to foamed aqueous fluids to be introduced into a well. More specifically, it is concerned with foam additives which lower the fluid loss of the foam during injection of the foam into a gas or oil well.
2. Description of the Prior Art
In most, if not all, applications where fluids are introduced into a well, fluid loss is a significant problem. In enhanced recovery techniques, differences in permeability of various zones can result in some formations being bypassed and not contacted by the driving fluid. Similar bypassing can occur during acidizing, with some portions of the formation not being adequately contacted by the acid. Though not normally so described, as used herein, the term "fluid loss" is intended to include such bypassing during enhanced recovery or acidizing.
Foams have a number of advantages, including generally lower fluid loss, and have been used in a variety of operations where fluids are introduced into a well.
In the past, aqueous foams have been used in hydraulic fracturing operations as described, for example, in the following U.S. Pat. Nos.: 3,136,361, issued to Marx on June 9, 1964; and 3,937,283, issued to Blauer, et al., on Feb. 10, 1976 (see also Canadian Pat. No. 1,000,191, issued to Plummer, et al., on Nov. 23, 1976).
Foams have also been used in well cementing operations, as disclosed, for example, in the following U.S. Pat. Nos.: 3,844,351, issued to Sutton, et al., on Oct. 29, 1974; and 3,299,953, issued to Bernard on Jan. 24, 1967.
Aqueous foams have also been used in enhanced recovery, as described, for example, in the following U.S. Pat. Nos.: 3,185,634, issued to Craig, et al., on May 25, 1965; 3,460,623, issued to Leach on Aug. 12, 1969; and 3,177,939, issued to Holm, et al., on Apr. 13, 1965.
Foams have been used in acidizing, as disclosed, for example, in the following U.S. Pat. Nos.: 3,174,929, issued to Andersen on Mar. 23, 1965; and 3,612,179, issued to Anderson, et al., on Oct. 12, 1971.
Other uses of foams have been in drilling operations, as disclosed, for example, in the following U.S. Pat. Nos.: 3,223,186, issued to Lummus, et al., on Dec. 14, 1965; 3,215,200, issued to Kirkpatrick, et al., on Nov. 2, 1965; and 3,297,098, issued to Elman, et al., on Jan. 10, 1967.
Typically, of course, these aqueous foams may contain a number of additives, both liquid and solid, in addition to the gas used for foaming. A large number of surfactants (or foaming agents) have been used with foams and the surfactants listed in U.S. Pat. No. 3,342,261, issued to Bond on Sept. 19, 1967, are typical.